A group of nodes is defined as a plurality of mobile nodes (MN) following the same move rules. Moving a group of nodes is referred to as a group move. Examples of some group moves include a tour group, passengers on a vehicle, and other small groups. Moving across a base station (BS) during the process of a group move is referred to as group handover.
One way to handle a group handover is through Layer 2 (L2). This method uses a radio unit (RU) for facilitating the handover of a group. The RU neither controls nor involves the communication between the group and the BS. It is merely configured to notify other equipment in the network (e.g. the BS) in advance that a handover is to be performed, so that the network is able to make preparations for the group move. Upon receiving the notification, the network accomplishes the handover after making some corresponding preparations.
In this solution, as the RU is not in communication with a mobile node, the information about the handover comes from the network or a Global Positioning System (GPS).
In IEEE 802.16j, an application scenario of a relay station (RS) is a mobile relay station (MRS), in which the RS moves together with a large number of Mobile Stations (MS), and assists the MSs to perform a handover.
Another technical solution defined in IEEE 802.16j is to bind new and old connection identifiers (CIDs) on the MRS to keep the old CID unchanged, so that the MS need not be aware of the handover. FIG. 1 is a schematic flow chart of implementing a handover by binding new and old CIDs on an MRS. Referring to FIG. 1, the handover process includes the following steps.
In step 101, the MRS sends a MOB_MSHO-REQ message to a serving base station (SBS) by using its own CID, so as to initiate a handover.
In step 102, the SBS sends a MOB_BSHO-RSP message to the MRS. Before sending the MOB_BSHO-RSP message, the SBS may send CIDs and media access control (MAC) addresses of all the MSs under the control of the MRS to a target base station (TBS) through a backbone network. The SBS receives an HO_ID returned by the TBS and carries the HO_ID in the MOB_BSHO-RSP message.
In step 103, the MRS sends a MOB_HO-IND message to the SBS.
In step 104, the MRS starts to hand over to a new link, and after a synchronization process, the MRS sends an RNG-REQ message for protecting the HO_ID to the TBS.
In step 105, the TBS assigns CIDs to MS1 and MS2 under the control of the MRS, and sends the CIDs to the MRS in an RNG-RSP message. The MRS establishes a matching relation between the new and old CIDs, and exchanges the new and old CIDs during uplink and downlink data transmission.
According to this solution, the RNG-RSP message delivered by the TBS needs to carry the new and old CIDs of all the MSs under the control of the MRS, so that this message may be over-sized.
In another technical solution, all the MSs under the control of the MRS first temporarily hand over to the TBS, then the MRS hands over to the TBS, and finally the MS hands over back to the MRS. According to this solution, problems resulting from an excessive number of handovers can be avoided.